A wireless mobile device can include one or more location-aware applications that are configured to perform location based tasks such as store finding and transit routing. Location-aware applications depend on positioning systems to determining a location of a wireless mobile device. One example of a positioning system is configured to incorporate a satellite positioning system receiver in a wireless mobile device and to specify a real-time location of the wireless mobile device by use of only signals from satellites in view. Satellite positioning systems can provide high accuracy, but require a clear line of sight between satellites and the wireless mobile device. In open sky areas where satellite positioning signals are not obstructed, the wireless mobile device can receive sufficient line of sight signals from satellites. However, satellite positioning systems are largely ineffective while a wireless mobile device is in shadow areas or in buildings. Further, receiving and processing satellite positioning signals may consume substantial energy and hence shorten battery duration.
Recent proliferation of access points in wireless local area networks (LANs) has made it possible for wireless mobile devices to use these access points as an alternative positioning system for location determination.